Hi there guys i have put loads of goodies on my mastercraft this winter and have realised i need to upgrade the alternator!! (After paddling back the other day!!) I have the LQ9 and according to the owners manual on mastercraft website the alternator is pushing out 51 amps at 2200 RPM and the upgrade is to a 90 amp Alternator at 2200 RPM.

Do you keep your boat on the trailer in the garage at night? Do you listen to the stereo loud while just sitting or only while riding? What type of batteries, how many and how are they set up?

Just to give you an idea the formula for calculating how many amps your boat requires to keep the batteries at a full state of charge is:

Watts/volts=amps

Assuming you have 2000 watts in your stereo you would need this amount of watts to keep fully charged.

2000/12=166.66 amps.

This is not entirely accurate because your system is actually going to be 12.6-13 volts I believe so you can drop the required amps. Also that equation is assuming the stereo is drawing the full 2000watts the whole time which it isn't. But then you have to add for the PCM, lights, electronic gauges, heater, shower and anything else that is drawing power from you charging system.

I am guessing that you have a Motorola style aternator since you say it is a 51 amp. That alternator only puts out 35 or so amps at idle. Idle being 2000 rpm. That is idle rpm of the alternator not the engine. Your engine probably idles around 600-700 rpm. With a 3 to 1 pulley ratio you are around 2000 rpm idle at the the alternator. The 90 amp alternator only puts out another 5 amps at idle, but at wakeboarding speed would put out close to that full 90 amps.

If I were you I would make sure I have a 2 battery system with 3 batteries. Make sure you have something to separate your starting and critical systems from your house bank. Makes sure you use all the same types of batteries(gel, agm, lead acid). If you really want to do it right get a starting battery(make sure it has enough CCA to start your boat easily). Then get a couple other deep cycle batteries to run in parralel to have the amps hooked up to. I would also install a battery charger on your boat so you can plug in the boat at the end of the day and trickle charge the house bank to keep charged and not damage the batteries.

Wow I think that is the longest post I have ever made. I do think there are too many people that think you can just add a cheap 150 amp alternator and solve all your problems.

Wow Brett you da man when it comes to alternators!!!! thank you so much!! I do have a 2 battery set up ad i have checked and i have a 70 amp alternator!! i have foud a company that can rewind the alternator for me to whatever i want!!! do you not think that doing this will solve my problems??? i was thinking about getting a Optima battery also (have 3) just to run the sound system!! what do you think???

Danny, that will probably help if you have the alternator redone. Don't get an optima battery if you have regular lead acid batteries to. Different types of batteries require different voltage and you can fry one battery and not charge up another.

Danny I have 3 JL amps (slash series) on my boat and I run 4 batteries for the stereo, and one for a reserve. You might think about adding some batteries to your setup. Are you charging them completely after every outing? You can't rely on your alternator to recharge them fully.

Danny, does it die from just sitting and playing the stereo or just running around wakeboarding and stuff? I don't know anything about the Schnapp batteries. What you want to do is have one battery that has a high CCA rating for starting, the pcm, and other critical components. Then get one big or 2 smaller deep cycle batteries with high 20 mp Hour ratings to be the house bank. You want to hook the main power and ground for your stereo/amps to this bank.

Use a product like a Sure Power part# 1314 to separate the banks. This product keeps the banks separate from each other. It also is set up to give priority to the bank of choice. You want the bank with priority to be the starting bank. It only charges that bank till it reaches a certain voltage and then combines the batteries and starts charging the house bank. This is nice because it keeps your critical systems charged so you don't end up dead in the water. This product is cheap and easy to install. Here is a link to the product.

I have never had to worry about charging them before adding all this stuff!!! i think i will upgrade the Alternator and add another battery and hope that cures the problem!! i think i will try and push 180 amps on the alternator! I think the sound system is pushing around 1800 watts and then the heater and hot shower also!!!

No Brett the batteries discharge just from running around the lake i was really careful about playing anything or running the heater and stuff while the boat was not running!!!! it took the whole day but the battery warning signal came on!!!!!

Danny you need to charge the batteries at the end of the day, or before you take the boat back out. They aren't getting charged back up with the alternator, and the alternator can't keep up with the current draw of the amps. If I were you I'd add another battery, leave the alternator as is for now, get a good battery charger and be diligent about charging them after every outing. If you do this I doubt you'll have any more problems.

180 amps out of a small frame alternator is a lot. My guess is the heat that is going to cause will fry that puppy quick. Just a though but if you are running your shower don't have your stereo cranked and the same with the heater. Although I do realize you may have the heater on while you are riding or cruising and that is when you would want the stereo cranked up.

I like nu bu's setup of having 3 or 4 batteries all in parallel to run the stereo.

Danny no power does pose a problem then. I'm sure someone on here has a good idea of how to charge your batteries back up without access to a power supply. Maybe the big alternator is going to be your best bet. Balmar makes some HO alternators that put out up to and over 200 amps.

Brett, with that Sure Power separator I assume it is best to work with the stereo wired to the house bank only? I currently have a perko switch and only two batteries but I think I need more power.

With three amps I think I might be pulling too much from my current system. I see the volt meter in the dash jump on bass hits. So I want to add a third battery and maybe some sort of separator. So if I do that I wonder if I should move all amp connections to the two stereo batteries?

I already have a great 3bank charger onboard I hook to the batteries at night on the dock.

That is correct Bill. You should have all the amps wired just to your house bank. What I tell people about the battery selector switches is did you buy a 50k boat have to lift a cushion and flip a switch. The Sure Power unit is a little over $50 and works better than an isolator and isn't really more expensive.

going to a bigger alternator will help but still even at a 100-120 amp (which is about the most you can get from your small frame alternator w/o spending a grand) alternator it will not charge your batteries up. Alternators will usually at most maintain a charge and charge a little maybe with NOTHING running but the motor. I would clearly get 3 batteries at least with your 4 amp setup. Checkout Lifline batteries, or other sealed agm or gel batteriers. 2 in paralell and then a third separated with a perko or something for starting only or a reserve to get you home. If you are running a big system you MUST use a battery charger to charge them back up after running them down no matter how big your alternator is it will not charge them back up to 100% like an overnite trickle at 10+amps. If you store it in the water you may be forced to take them out at night and bring them to shore for an overnite charge or get a small honda quiet generator and get 15-20 amp speed charger and let that thing run while you get all loaded up or at least for a couple of hours some how. Lose the Scnepps for sure. Good luck

Brett, totally hear you on the switch flipping…I assume that can then just take the place of the perko?

I have the stock two battery option from Supra…I know they are interstates but I’m not sure what kind – one is a cranking and the other a deep cycle. Do I need to make sure I add the same type of battery to the system as the other two….or do I NEED to replace them all?? I thought I would just go buy another similar type deep cycle and install parallel to the current deep cycle.

My charger can handle different types, but I think they all need to be the same: http://www.promariner.com/productFeature.php?ProductNum=42021. I just installed it next to the batteries, since I have on-dock power I just plug it in after coming in. But I can’t leave it plugged in overnight since it says it needs ventilation and I don’t want to leave the boat uncovered all night…I don’t know how important the ventilation is but I figure better safe than sorry…

Bill, you do want to make sure they are all lead acid if that is the way you wanna go. I would not just add a new battery to the house bank side though. Adding a new battery to an old one in the same bank can shorten the life of the new one. I would add 2 new batteries wired in parallel to the house side. My company does very good with Deka batteries and they have all the options of lead acid, gel or agm batteries. If you can get me the part number of the starting battery I can see if I can get something that is compatible in Deka at a good price.

I also carry the Sure Power product. I forgot to mention the 1314 is rated at 100 amps so it should be fine with a stock alternator.